Heat-sealed caps have the advantage of being very cheap, sealing very tightly, and providing a clear indication of tampering. The standard procedure for capping a bottle is to move a succession of the bottles through a station where the caps are set atop them, and then to a heat sealer where the caps are sealed under application of pressure.
In the upstream station where the caps are set on the bottles, it is standard to stack the caps, which are thin foils or films, in a magazine or supply whose bottom is open. At this supply, a grab pulls a cap off the bottom of the stack and sets it accurately atop a bottle, normally while same travels through the station.
In the heat-sealing device, a pressure is applied to the top of the bottle and simultaneously, to the heating of the caps, those being thus heat sealed to the rims of the containers.
The caps are formed of a suitable heat-sealable material or have a suitable heat sensitive coating which is operative when heated to effect a seal to the rims of the containers.
The main problem with such devices is that the cap shifts or falls off the bottles before they can be heat sealed in place. The caps are typically very light and fit fairly loosely on the bottles, so that keeping them in position is not simple. On the other hand, if the cap is lost the package being made is normally ruined and must be rejected.
In U.S. Pat. No. 3,908,340, the caps are displaced continuously, that is without stopping through the station where the caps are emplaced and a device is used to tack-weld the caps on, immediately after they are positioned. Such an arrangement represents an improvement on the known systems, but nonetheless, still produces excessive rejects where the cap has shifted or been lost.
Furthermore, it is not possible to effect the heat sealing at the supply, since this heat sealing implies the application of a pressure which is not compatible with the structure of the grab which effects a 180.degree. rotation.